does anybody know if there is a word or measurement that describes that
efficiency at which a substance traps longer waved solar radiation?
For example glass is pretty good at trapping heat, so that may be rated at
100 "Scovillage" units or possibly it could be described as having a
"Maxwell" rating of .5 celsius per second per cubic meter. Polycarbonate
also used for green/glass houses may have a similar values while brick or
other opaque materials would be close to zero. What would the real term
for Scovillage or Maxwell be?
If it what you want is truly a measure of efficiency, then it would be
unit-less. (It's just a ratio)
The energy of one 680 nm photon is:
E = hc/?
Photosynthesis requires 59 kJ per mol of ATP. Meaning that:
EATP = 59 10 3 J mol-1 / 6.022 1023 mol-1 = 9.80 10-20 J per ATP
So, the energy efficiency of photosynthesis is:
= 9.80 10 -20 J /2.92 10-19 J = 0.34 or 34%
there is specific heat capacity
ability to absorb infrared and NOT re-emit it. CO2 and methane CH4 have very
absorption/retention rate way beyond ability of individual atoms.
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I would be surprised if there were such a term because the greenhouse
effect is not a property of the material alone. The obvious (to me, at
least) variables are:
1) The spectrum of the incoming radiation. For an incandescent
source such as the sun this is mostly determined by the source
temperature. (The "surface" of the sun is about 6000 K) But
atmospheric absorption figures in this as well.
2) The spectrum of outgoing radiation. This is mostly determined
by the temperature reached by surfaces inside the greenhouse.
3) The transmission coefficient of the glass at every wavelength.
Also, it is not meaningful to talk about the greenhouse effect with
opaque materials as there is no radiation passing through. (Unless you
want to talk about x-rays and gamma rays.)
A L B E R T A Alfred Falk firstname.lastname@example.org
I didn't like my chances, either, but I thought I'd ask anyway. To
clarify, I'm looking for a term that enables comparisons of different
materials for use in a greenhouse application. The term/measurement
doesn't necessarily have to have mathematical precision, but if there is
a directly measurable value that's good too. Something like R- values
for building insulation in the US, or PR/+ ratings for microprocessors.
If the E in low E (emissivity) glass is quantifiable (even with some
fudging allowed) and not just some vaccuous idea, then that's probably
exactly what I'm looking for.
Seems polycarbonate is widely used, but is that because of superior
trapping or a combination of trapping, structural strength, price and/or
other?. I'd also like to see how Lexan, plain plexiglass, clear PVC and
one other clear plastic (don't remember off hand) compare solely from a
heat trapping / heat retention perspective.
I'm jumping back 30 years or so, but I think the ASHRAE Manual
[American Society of Heating & Refrigeration mumble-mumble] has a
table with material's emissivity and absorbtion rates. [and 'transfer
rate' might be a separate table]
The only part of it I remember offhand is that unglazed brick is very
similar to human flesh-- that's why we think of it as 'warm'.
The 'E' in 'E-glass' *is* quantifiable-- though I'm not sure if all
manufacturers use the same standards yet. [they didn't in 1970] The
emissivity is how much of the heat gets passed through-- not how much
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